The present invention generally relates to packings for pumps and, more particularly, to improved packings which are especially adapted for sealing the working side of the reciprocating piston in a pump for liquids such as water-based solutions or suspensions. In this regard, an important embodiment of the present invention is directed to an improved unitary packing wherein a generally concave or cup-shaped packing member includes an outer cylindrical annular flange and is otherwise structured, including a radially extending annular lip, to complementarily overlie the working side surface of the piston of a positive displacement chemical feed pump, the generally concave working surface of the packing being the liquid-contacting surface when the pump is in use.
Packings in combination with the working side of a piston within a reciprocating, liquid transporting pump have heretofore been employed in a wide variety of applications. In general, it has been found advantageous to provide these packings in a generally concave or cup-shaped form and to install them over a generally concave working side of a reciprocating piston to enhance the seal provided between the annular extent of the piston and the wall or lining of the pump cylinder within which it is fitted, such packings being made of somewhat elastomeric material in order to enhance the seal between the piston and the cylinder lining. Such packings, when originally formed and initially installed, are usually not in close overlying relationship with substantially the entire generally concave working side surface of the piston, primarily because the non-working, convex surface of such known packing assemblies are substantially hemispherical throughout while the concave working side surface of the piston has a generally hemispherical configuration which is terminated at its annular extent by a radially extending circumferential lip, whereby the substantially entirely hemispherical surface of the packing assembly does not closely overlie the generally concave surface of the piston substantially throughout the entire extent thereof. Consequently, after a pump incorporating such a packing assembly is in use for several hours, the packing will begin to deform, primarily by cold flowing, into the free space that existed between the initially structured hemispherical surface of the packing assembly and the generally concave surface of the piston. Experience with such arrangements has indicated that this free space left upon initial installation permits the heretofore mentioned cold flow as well as an attendant interference between the packing assembly and the cylinder lining and a detrimental stress on the structure, resulting in a distortion of the sealing surface of the packing assembly and a failure of the assembly to provide the sealing function between the piston and the cylinder for which it is intended.
In accordance with the present invention, the foregoing problems and disadvantages of these reciprocating pump packing assemblies have been overcome through the use of packing assemblies that include an axially extending outer annular flange throughout the annular extent thereof such that a radially extending circumferential lip is formed where the generally convex surface joins the annular flange, whereby the packing assembly closely overlies the working side surface of the piston. As such, any free space between the mating surfaces of the piston and the packing assembly is substantially eliminated so that stresses and interferences between the cylinder lining and the annular extent of the packing are significantly reduced from those found in hemispherically shaped packing assemblies in order to greatly extend the working life of the packing assembly. Furthermore, the working life of the packing may be extended even further by structuring the packing to have the ability to intermittently rotate somewhat about its axis in order to significantly reduce wear along the outer surface of its planar annular flange which would otherwise be caused by an invariable orientation of the packing with respect to the cylinder lining, thereby permitting any imperfections such as occulusions or burrs on the cylinder lining to score or otherwise damage the annular flange of the packing assembly upon several hours of reciprocating movement.
It is, therefore, an object of the present invention to provide an improved packing.
Another object of the present invention is an improved packing which is especially suitable for use in piston and cylinder pumps for liquids, particularly hot aqueous liquids.
Another object of this invention is to provide an improved piston packing which includes an outer cylindrical annular flange structured for sealing communication with the cylinder lining of a pump.
Another object of the present invention is an improved unitary packing member having a generally convex surface that is structured to closely overlie the generally concave surface of a reciprocating piston in a pump to reduce stresses in and to extend the working life of the packing member.
Another object of this invention is an improved unitary packing member that is rotatable about its axis to minimize scoring thereof by imperfections in the piston wall which can lead to failure of the packing assembly.